This invention relates to a laser amplifier system and method capable of amplifying laser beams of elliptical cross-section of high eccentricity.
Prior art laser amplifier systems have either used a single laser beam of circular cross-section amplified in a laser amplifier segment of circular cross-section positioned perpendicular to the propogation axis of the beam or have used multiple passes of a circular cross-section laser beam through different portions of a circular cross-section segments positioned at the well known Brewster angle to the direction of propogation of the beams. Furthermore, it is standard practice in commercially available segmented disc amplifiers to use a laser beam of circular cross-section and disc amplifier segments of elliptical cross-section to satisfy the Brewster angle orientation configuration. This latter configuration has superceded the two previous configurations which utilized circular cross-section beams and disc segments due to the fact that it is matched for Brewster angle operation.
However, with the advent of high power lasers it was realised that relatively low damage thresholds in the amplifier segments meant that the laser beam to be amplified had to be diverged to spread out the load so as to operate the amplifier below damage flux density. This fact meant that the aperture area of the amplifier segments had to be increased to accommodate the expanding beam undergoing amplification. It has been found that large laser systems are limited in beam diameter by the size of amplifier segments that can be used. These segments are of elliptical cross-section and it is the length of their major axis which determines the maximum diameter of the circular cross-section laser beam to be amplified. On the large neodymium-glass lasers now in operation, the size of the elliptical cross-section amplifier segment is limited by its major axis which exceeds the self-oscillation threshold at about 40 cms. This in turn limits the diameter of the circular cross-section laser beam to about 25 cms. Since much larger area beams are required from high power lasers either one needs a much better laser medium from the viewpoint of damage threshold, travelling wave excitation of laser media to supress parasitic oscillations prior to the arrival of the laser beam or more effective utilization of current technology. The present invention provides for better utilization of current technology with a laser beam of elliptical rather than circular cross-section.